JRFisher

I have built ARF's, Kits, and planes from plans. Now I would like to try my hand at a true scratch build.

How do I start? I was thinking along the lines of a Funfly profile with a tapered wing.

Any help would be appreciated.

BMatthews

First you need to design it. Whether you just keep some numbers in your head and wing it from there or put some lines on paper it still needs to have a shape and areas that make sense to the air. For some links to sites with design theory check out the sticky threads at the top of this section as well as the Aerodynamics section. But for a funfly profile you're probably just as well off to copy one that's already out there and just alter the shape of the fuselage slightly to get it to look like what you want.

Other than that the size is usually based on folling the expample of something you have already successfully flown or based on what other folks have done. And the internal structure is similarly based on what you have done before and from studying other folks plans.

Campy

My Feedback: (1)

I suggest getting a set of plans from a reputable source and doing a plane from the plans before trying your hand at designing a plane.

JRFisher

Campy- I have built planes from plans twice now.

I'm looking to expand my horizons by doing a true scratch build.

How do you determine CG?

How do you design wing placement? (Fore and Aft position in fuse)

Campy

My Feedback: (1)

BMatthews

It's a guess based on previous models and experience. You base it on the weight of radio gear and engine countered against the weight of the fuselage and tail that you think you can make it to. This is why we often have to shift the gear around or add nose or tail weight because we guessed wrong.

For your first own design I strongly recomend that you draw your own plans to get all this sort of right. Drawing plans will let you see what your guesses look like and with some of the basics down you can work on the details in an orderly fashion.

We've all seen posts here made by folks that build models using nothing but an image in their mind but all of those folks are long time scratch builders that can strongly visualize all the details thanks to a lot of experience. But even those folks would not build anything truly advanced without a plan. Rectangular sections are fine but if you start playing with curves and bent surfaces you pretty much need a plan to work from or there'll be a lot of lost time and ruined parts.

dicknadine

do you want to design your own plane or enlarge small 3 veiws of some existing aircraft?? sugest that you start with finding a airplane that you like, either old time/vintage. find a smal 3 view of the plane that you like and enlarge it to your wing span. then start becoming a model airplane structural engineer. it takes a lot more experience than one or two kits. also once that you have drafting experience you start buying your balsa in bulk lots and learn how to shape it to fit your plans. it ain't simple-- it takes time - trial and lots of errors. dick stamm

AeroDave

I started designing and scratch building glow powered funfly/3D models about 5 years ago. I had decades of kit building experience so i figured I knew what was needed interms of structural design. I bet I built a good dozen variations of my "design" until I got one that really flew the way I wanted it to. I learned over time the effect of changes to tail moment, hieght of the stab, stuff like that. They all flew (except one, long story) but some had some really odd tendencies in the air. I really had a lot of fun, building one, trying it out and then taking all the gear out to try and build the next one just that much better. Until last weekend, all I had were hand tools. Ribs took so long to cut out. And dealing with lite ply was a real chore. Then Saturday my wife went shopping and came home with a new band saw, scroll saw and disc sander! Good girl! So of course, I started building right away. This new one is looking good!

Anyway, I write all this to say go for it! I didn't know what to do or how to start, so I just started. At least by doing it wrong, I had something to fix. I woud say this: for your first one, try to model your design after something that already exists in terms of wing span, area, airfiol and moments. That way you'll be sure you'll get something that will at least fly.
Most of all have fun! Designing and building your own models will become a great source of pride and satisfaction.

Best of luck,
Dave

markswa

I Does anyone know of a guide that I can download to help me with my first scratch build ?

Balsa Shavings

Ahhhhhh, Scratch Building, It's Like A Rollercoaster Ride, Fun One Minute, Then Hurling The Next, When You Relise You Just Made 2 Lefthand Wing Panels And Neither One Fits Like Your Plans Show. But There Is Nothing Like The Feeling Of Showing Up At The Flying Field, With A New Plane, And Everbody Asks You What Kit Is It, And You Say, No Kit, I Designed It And Built It From Scratch. I Have a Box Full Of Mistakes, But Never Give Up.

AeroDave

ha ha. That's right! I was working on a 120 sized aerobat this weekend. I had the fuse sheeted before I realized the slot where the horizontal stab fits was off by a couple of degrees and the incidence for the stab was going to be off. I had to dig in there and fix everything, but since it was something I scratch built, and designed, i was able to re work it fairly easily to the zero zero I had originally intended. I tell you though, even with mistakes, redos, whatever, I wouldn't trade scratch building and designing for anything!

Balsa Shavings

Amen To That!!! I'm Working On A 1/2A Waco SRE To Fly In My Front Yard. 200' X 700' All Centipede Grass. The Down Side Is That It Is Surounded By 150' Tall, Plane Eating Pine Trees.